Darwin, however, owed much to his many predecessors and to his contemporaries. Among them the British biologist Alfred Russell Wallace, who independently and almost simultaneously arrived at the idea of natural selection for which Darwin is often given credit. Darwin's basic theory remains today a fundamental part of the evolutionary concept. However, far more information is available to modern biologists than what was known to Darwin. When the laws of Heredity, formulated by the Austrian monk Gregor Mendel, were rediscovered in 1900s, it became necessary to modify idea of natural selection in order to emphasize the role of inheritable variation and the need for geographic isolation, in the origin of new species.
Charles Darwin is generally given credit for having done two things. Firstly, for having set forth the theory of organic evolution, that is, the evolution of each species, and, ultimately, from one or a very few original forms. And second, for being the first to propose the satisfactory explanation of how the origination of species occurs. This explanation is the theory of natural selection. We must distinguish quite carefully between the theory of evolution, as such, and the theory of natural selection, which is concerned with the means or mechanisms involved in the evolutionary process.
Given their two million-year-plus life span, the Australopithecine were surely one of evolution's better experiments. But nature is an inveterate tinkerer, even with successful species. First lived the Ardipithecus ramidus; it is not yet known whether it walked upright is still unknown. Then came the A. anamensis were considered to be walking upright. Next is the A. afarensis. To date, found only in Eastern Africa. Most famous example is Lucy. A. africanus was the first human ancestor to be discovered in Africa. Came the existence of A. aerthiopicus, A. garhi, A. boisei and A. robustus.
